1. Field of the Invention
The present invention relates to a laser diode driver and driving method for driving a laser diode in an optical recording/reproducing apparatus, and more particularly, to a driving of a laser diode driver performing auto laser power control (APC), an optical pickup device and an optical recording/reproducing apparatus and method using the same.
2. Description of the Related Art
In modern society, also called “The Information Age or Multimedia Age”, recording media having high capacity, such as magneto-optical disk drives (MODDs), DVDs-RW, or DVDs-RAM, have become strongly relied upon. Optical recording/reproducing apparatuses use a laser diode (LD) to generate a laser signal for reading/writing information from/on optical recording media. The laser diode has input/output characteristics which sensitively change according to its operation temperature.
In other words, changing or using different inputs (generally represented as a value of currents) becomes necessary for outputting laser signals having the same power level corresponding to operation temperatures of the laser diode. Thus, an auto laser diode power (APC) control technique, which determines the general performance of the optical recording/reproducing apparatus, to control the laser diode to be in an optimal state, is required.
Further, optical recording apparatuses use storage media with high capacities and densities and perform recording/reproducing operations at a high-transfer rate. Thus, APC devices must be protected from potential noise and interference.
FIG. 1 is a block diagram of a laser diode driver 100 currently used in most optical recording/reproducing apparatuses. The laser diode driver 100 includes switches 10a through 10c, a multiplexer 12 for multiplexing powers of the switches 10a through 10c, an amplifier 14 for amplifying an output power from the multiplexer 12 with a predetermined amplification gain, an adder 16, and a high frequency modulator 18 (hereafter referred to as “HFM”).
Currents, peak current, bias current, and read current, or voltages, hereinafter referred to as “drive potentials”, corresponding to power levels of a laser diode (peak power level, bias or erase power levels, and read power level) are applied to the switches 10a through 10c, respectively. The drive potentials are turned on/off by a peak power control signal, a bias power control signal, and a read power control signal, respectively. For example, a peak drive potential necessary for generating the peak power level is turned on/off by the peak power control signal.
The output power signals of the switches 10a through 10c are multiplexed by the multiplexer 12. The output power signal of the multiplexer 12 finally becomes a laser diode drive signal LD DRIVER_OUT which has a waveform including a first pulse, a recording pulse, a multi-pulse, and a last pulse. The laser diode is then driven by the laser diode drive signal LD DRIVER_OUT to generate the recording pulse.
However, the laser diode cannot be fully driven by only the output power signal of the multiplexer 12. Thus, the output power signal of the multiplexer 12 has to be amplified by the amplifier 14.
The HFM 18 generates a high frequency modulation signal for removing light interfering noise from an optical detector (not shown). The high frequency modulation signal is added to the output power signal of the amplifier 14 by the adder 16. The laser diode is then driven by the output power signal of the adder 16. Here, the high frequency modulation signal is set to have the most effective frequency and amplification to remove potential light interfering noise. The high frequency modulation signal is mostly used in a read mode.
The laser diode driver shown in FIG. 1 may include 2-5 switches according to a number of used channels, i.e., 2-5 channels according to the number of power levels used in the recording pulse.
FIG. 2A is an illustration of a CD-RW recording pulse (a 3-channel example), and FIG. 2B is an illustration of a DVD-RAM recording pulse (a 5-channel example).
Referring to FIG. 2A, illustrated portion (a) represents input NRZI data, illustrated portion (b) represents a recording pulse for forming a predetermined recording mark, illustrated portion (c) represents a read control signal, illustrated portion (d) represents a peak control signal, illustrated portion (e) represents a bias1 control signal, and illustrated portion (f) represents a bottom control signal.
Referring to FIG. 2A, illustrated portion (a) similarly represents input NRZI data, illustrated portion (b) represents a recording pulse for forming a predetermined recording mark, illustrated portion (c) represents a peak control signal, illustrated portion (d) represents a bias1 control signal, illustrated portion (e) represents a bias3 control signal, illustrated portion (f) represents a bias2 control signal, and illustrated portion (g) represents a read control signal.
The control signals control the drive potentials so as to obtain the laser diode drive signal LD DRIVER_OUT having the same waveform as the recording pulse shown in illustrated portion (b) of FIGS. 2A and 2B, for example.
FIG. 3 is a graph illustrating characteristics of an example laser diode, i.e., input/output characteristics of TOLD9452MB made by TOSHIBA. In FIG. 3, it can be seen that the laser diode has input/output characteristics which change with a change of temperature. Typically, an operation temperature of a laser diode increases after a certain period of time while the laser diode is driven, whereby optical output power decreases corresponding to the input current. For example, when the input current is 110 mA, the optical output power may be 40 mW at an operation temperature of 25° C. However, the optical output power may be reduced to about 20 mW at an operation temperature of 70° C. Therefore, a failure to control the laser diode according to changes in the operation temperature causes malfunctions during recording/reading, and may even make recording/reading impossible.
One way of solving this problem is to use an APC device. The APC device feeds a change in the output power of the laser diode back to the laser diode, to uniformly maintain the output power of the laser diode.
However, in the prior art, the APC operation cannot be realized within the laser diode driver, but requires an additional circuit or IC. An APC device is generally installed on a Main PCB, with the laser diode driver being positioned in an optical pickup. The Main PCB may be connected to the pickup via a flexible printed circuit board (FPCB).
The APC device is supplied with a monitor signal mon-PD from a monitor photodiode (PD) attached to the laser diode via the FPCB. The laser diode driver also has to be supplied with control signals via the FPCB.
Since the monitor signal mon-PD is very small, e.g., of about several μA, it is highly sensitive to noise. The frequency of a control signal is very high, thereby causing electromagnetic interference (EMI) in peripheral devices. For high recording density, the wavelength of the laser signal has actually been shortened to 780 nm (in the case of compact disks), 635 nm, 650 nm (in the case of digital versatile disks), and 410 nm (in case of HD DVD using a blue laser). The recording/reproducing transfer rate is commonly up to 52×. As a result, the frequency of the control signal has increased. Thus, due to EMI, recording performance may be deteriorated and an accurate interface via the FPBC may be impossible.
When the recording/reproducing apparatus includes a plurality of laser diodes to maintain the compatibility between recording media, the recording/reproducing apparatus has to include additional circuits and parts, such as APC apparatuses, laser diode drivers, and the like, corresponding to the respective laser diodes. Thus, it has become difficult to reduce size, weight, and price of recording/reproducing apparatuses.